A corrugating medium is fluted by passing a web of such medium between heated, fluted rolls and applying high pressure to deform the web. An adhesive, preferably a semi-gelled starch mixture, is then applied to the crests of the corrugated medium. A smooth web of a linerboard is pressed against the glued crests by a heated pressure roll to form single face corrugated paperboard. Conventionally, both webs have been subjected to successive heating and preconditioning to render the material malleable and to set the adhesive during the instant when the pressure roll, the liner and the glued crests of the medium are juxtaposed.
The corrugating rolls are provided with longitudinal flutes which act as dies to corrugate the medium and constitute the means by which one corrugating roll drives the other corrugating roll. It is conventional to drive the lower corrugating roll by a motor and a right angle speed reducer as exemplified by the last two mentioned patents.
The corrugating process or the tucking of the web medium into the flutes of the corrugating rolls exert intermittent and erratic tensile stresses on the medium. This causes many mediums to be strained beyond their elastic limit, particularly at high operating speeds. Accordingly, means have long been sought to attentuate and/or equilize the tensile stresses on the medium. One early attempt to control this problem is described in U.S. Pat. No. 1,810,930. The last-mentioned patent provided a feeding means to feed the medium under slight but constant tension. Another attempt is disclosed in U.S. Pat. No. 3,479,240 which employs a capstan to provide a slight overfeeding of the medium. Neither of these feeding systems was particularly successful because the tensions on the medium were induced by the labyrinth of the meshing flutes beyond the range of an exteriorly mounted tension controlling device.
Many years ago, it was conventional to drive one corrugating roll of a single facer machine and gear the shafts for the corrugating rolls directly together so that they remain in mesh and rotated in opposite directions to corrugate a web passing therebetween. An example of such apparatus is shown in U.S. Pat. No. 2,576,281.
The flutes on a corrugating roll of a single facer machine are not involute and tend to rotate at non-uniform velocity. The teeth on meshing gears are involute and rotate with uniform velocity. Hence, driving both corrugating rolls with directly meshed gears results in erratic stresses being set up in the teeth of the gears and in the flutes of the corrugating rolls whereby commercially acceptable boards cannot be produced. Such problems do not exist when one corrugating roll is driven directly by a motor and said one roll drives the second corrugating roll through the mesh of the flutes. Structure of this type has been conventional in recent years. For an example of the last-mentioned apparatus, see U.S. Pat. Nos. 3,053,309 and 3,776,029. However, when this is accomplished, substantial tension is applied to the web being corrugated.
Some inexpensive web materials cannot be corrugated due to the amount of tension applied by the flutes of the corrugating rolls. In the so-called cold corrugating system, wherein the rolls are at room temperature, it is necessary to apply some type of lubricating medium such as wax to the medium before it is corrugated.